1. Field of the Invention
The present invention relates to a rotary crusher for crushing waste metal products such as, for example, compressors, air conditioners or refrigerators, particularly those containing combustibles. More particularly, the invention relates to the rotary crusher in which exhausted smoke can easily be treated and in which gas concentration can be precisely monitored to prevent an explosion.
2. Description of the Prior Art
In the conventional recycling of wasted metal products including iron and copper, the products are broken into adequate size and then the iron and copper materials are separated therefrom by, for example, a magnetic separation technique. In crushing the waste metal products, a rotary crusher is generally used to facilitate the subsequent separation process. The rotary crusher has a rotor with hammers mounted on its periphery so that the waste products can be crushed while being compressed by the hammers.
If the crusher breaks oil-containing metal wastes such as compressors, smoke arises in the crusher. The smoke travels having ridden on an airflow generated by rotation of the rotor and then emerges from an outlet of the crusher together with crushed pieces. Therefore, an exhaust processor having a ventilation fan is generally placed near the outlet of the crusher in order to collect the smoke.
When metal wastes containing a flammable material such as oil is crushed, explosion may occur. Accordingly, the crusher needs an explosion-proof system. Hitherto, the explosion-proof system is implemented by, for example, blowing inert gas or water vapor into the crusher according to the concentration of oxygen in the crusher that is detected by an oxygen sensor to maintain the oxygen concentration under the explosion limit. Such an explosion-proof system is disclosed in, for instance, Japanese laid-open patent publication H6-226137.
However, the conventional rotary crusher has the following drawbacks:
(1) In order to vent the exhausted smoke from the crusher completely, the inlet capacity of the ventilation fan must be greater than the exhaust capacity of the crusher. Accordingly, increase of the exhaust capacity of the crusher by, for example, increasing the speed of rotation of the rotor results in necessity of use of the suction ventilation fan having a higher inlet capacity. This in turn increases the size of the exhaust processor. Also, the exhaust processor with such a high inlet capacity fan may draw in light-weight pieces such as, for example, insulating paper or copper together with the smoke. The pieces caught by the fan do not only bring about clogging of the fan, but also reduce the waste recycling efficiency.
(2) The concentration of oxygen or flammable gas near a crushing point should be precisely monitored by, for example, an oxygen sensor to prevent explosion from taking place during crushing. When the oxygen sensor is placed in the crusher, the sensor should be disposed in a recess or protected with a cover to avoid its breakdown by collision with the crushed pieces. However, since the air stream is apt to stay in the recess or in the cover, the gas concentration tends to become uneven. Therefore, in the conventional crusher, an accurate measurement of the oxygen concentration has been difficult to achieve.
(3) When the explosion-proof means such as introduction of inert gas or water vapor is employed, pipes and nozzles must be installed in the crusher to introduce the gas. This complicates the construction of the crusher.
It is accordingly an object of the present invention to provide an apparatus, and a method of operating such apparatus, for crushing products containing flammable material, in which an exhausted smoke can easily be processed and in which gas concentration can be precisely monitored to prevent an explosion.
Another object of the present invention is to provide a recycling system that has a high recycling efficiency and that is safely operable.
In accordance with a first aspect of the present invention, a crushing apparatus comprises:
a rotor having a crushing means on a periphery thereof;
a casing for enclosing said rotor, the casing having an inlet and an outlet for materials to be crushed;
exhaust-circulating means for returning a part of exhaust gas from the outlet to the inlet of said casing; and
exhaust-processing means for ventilating and processing the exhaust gas exhausted from said casing.
The advantage of this invention is the ability to reduce the exhaust capacity of the crusher casing. This downsizes the exhaust-processing section of the apparatus and prevents the exhaust-processing section from sucking light-weight crushed pieces, thereby allowing a smooth operation of the crushing apparatus.
Preferably, the crushing apparatus comprises a gas sensor disposed in a gas pathway of said exhaust-circulating means. This arrangement makes it possible to measure accurately a gas concentration in the crusher casing.
Further, the crushing apparatus preferably comprises water-supply means for supplying water according to an output signal from said gas sensor in the gas pathway or near a terminal of the gas pathway of said exhaust-circulating means. By arranging the water supplier in such a manner, an explosion during crushing can be prevented with simple construction.
More preferably, the crushing apparatus comprises a crushed-piece sensor for detecting pieces sucked by said exhaust-processing means, an outlet smoke sensor for detecting leaked smoke without being sucked by said exhaust-processing means, and an inlet smoke sensor for detecting leaked smoke from the inlet of said casing of the apparatus. These sensors facilitate smooth operation of the crushing apparatus.
In accordance with another aspect of the present invention, method of operating the crushing apparatus is characterized in that:
if the crushed-piece sensor detects the crushed pieces, an inlet capacity of said exhaust-processing means is reduced until said crushed-piece sensor does not detect the pieces, but;
if the outlet-smoke sensor detects the smoke, a circulating capacity of said exhaust-circulating means is increased to within a range in which said inlet-smoke sensor does not detect the smoke.
In this manner, the smoke leakage from the inlet and outlet of the crusher casing is minimized, so that suction of the crushed pieces by the exhaust-processing means is prevented.
Preferably, if the gas concentration measured by the gas sensor is higher than a predetermined value, the water-supply means operates. This infallibly prevents an explosion which would otherwise occur in the crusher.
More preferably, if the gas concentration measured by the gas sensor is still higher than the predetermined value after a predetermined period from the start of operation of the water-supply means, the crushing apparatus stops operating. This further lowers the possibility of occurrence of the explosion.
In accordance with still another aspect of the present invention, a waste-recycling system comprises:
a crushing apparatus of the present invention;
a transport means for transporting crushed pieces exhausted from said crushing apparatus; and
a magnetic separator disposed above said transport means to collect ferrous components from the crushed pieces. In the waste-recycling system, suction of the crushed pieces by the exhaust-processing means is prevented. Accordingly, the waste-recycling system is smoothly operative and has a high recycling efficiency. Also, since a precise forecast of an explosion is possible, the system can be operated safely.